When first starting out, I think relaxed games that help a player get used to left and right directions (side-scrolling or platform) and timing on the controls is a good start. Then evolve into camera and movement based controls.
My suggestions are starting with these:
My Brother Rabbit
The Between Gardens
Dawn (may have some camera control, but this is the most relaxing game I’ve played for that)
Then move on to these:
La Rana
The Room Series
Aim Labs or any shooting game that has tutorials/ practice mode (for FPS practice)
These games are found on steam. Note, most of these are casual/puzzle based.
I don’t have much experience with co-op, so can’t help you there. But I do like the suggestions so far based on reviews.